Microfibrillated cellulose (MFC) (also known as nanocellulose) is a material made from cellulose fibers, where the individual microfibrils have been partly or totally detached from each other. MFC is normally very thin (˜20 nm) and the length is often between 100 nm to 10 μm. However, the microfibrils may also be longer, for example between 10-100 μm.
MFC can be produced in a number of different ways. It is possible to mechanically treat cellulosic fibers so that microfibrils are formed. The production of nanocellulose or microfibrillated cellulose with bacteria is another option. It is also possible to produce microfibrils from cellulose by the aid of different chemicals and/or enzymes which will break interfibrillar bonds or dissolve the fibers. One example of production of MFC is shown in WO2007091942 which describes production of MFC by the aid of refining in combination with addition of an enzyme.
MFC can be used within many different fields. In the papermaking industry it can both be added to the surface of a paper or board or to the furnish. It has been shown that addition of MFC can increase the strength of a paper or board. When used in paper coating applications, it replaces the synthetic or natural binders such as starch. Since the MFC has a very shear-characteristic effect at low and high solid content, it can be used to as thickening agent and/or water retention aid. However, it can also be used in many other technical fields, such as the food industry, polymer or plastic industry, paint, composite industry (e.g. cement), rubber industry, cosmetic and pharmaceutical industry.
A dispersion comprising MFC has the appearance of a highly viscous, shear-thinning transparent gel at low dry contents. Normally, a composition comprising MFC with a consistency of about 4% and higher is in the form of a very thick gel. Very fibrillated and fine material with high degree of polymerization might exhibit a gel like character at solid content about or less than 1 wt %. The gel has high viscosity making it very difficult to make it flow at low shear rates. This makes processing through pipes and pumps very difficult and thus also to distribute it to different end uses, for example to a surface of a paper or board substrate.
Moreover, it is often undesirable to add a composition with low dry content during production of paper or board to the surface of a substrate since it takes a lot of energy to remove the added water, for example during drying of the substrate. Another reason to avoid unnecessary addition of water is to save transportation costs, water and environmental impact (carbon footprint).
It is also possible to dry the produced MFC before addition to e.g. a pigment dispersion or wet end but this is a very energy consuming process and might have significant irreversible chemical and physical structural changes on the microfibrillated cellulose.
There is thus a need for a composition comprising MFC which has processable flow behavior and good colloidal stability at both low and high shear rates.